The Pentagon says the destruction of Syrian chemical weapons on board the U.S. cargo vessel MV Cape Ray began Monday.

Army Col. Steve Warren says it will take about 60 days, depending on the weather and sea conditions, to destroy the approximately 600 metric tons of material loaded onto the ship.

The Cape Ray left the Italian port of Gioia Tauro last Wednesday and is in international waters. The chemicals, including mustard gas and the raw materials for sarin nerve gas, are being put through special Field Deployable Hydrolysis Systems in the cargo hold to neutralize them. Last month Syria handed over to Western powers the 1,300 tons of chemical weapons it acknowledged possessing, completing a deal reached last fall under threat of U.S. airstrikes.

The resulting waste will be taken to dumps equipped to handle hazardous materials. U.S. officials say no vapor or water runoff will be released into the atmosphere or the sea.